The present invention relates to the use of xenon flash lamps in the manufacture of integrated circuit devices.
In the manufacture of integrated circuit devices various photolithographic processes are conducted. In such processes, a light sensitive material called a photoresist, is exposed by a flash lamp acting through a photomask, whereby a pattern is defined upon the photoresist. The optical lithography process is described more fully in U.S. Pat. No. 3,860,335 entitled OPTICAL SYSTEM which issued on Jan. 14, 1975 to Fausto Caprari and in an article entitled OPTICAL LITHOGRAPHY IN THE 1-.mu.M LIMIT, by D. A. Doane, Solid State Technology, August, 1980, pages 101-113.
The inventor has found that it is desirable to use a xenon flash lamp to expose photoresist material, because the light output of such a flash lamp is extremely effective in polymerizing the exposed photoresist. Unfortunately, xenon flash lamps designed specifically for use in semiconductor processes are not available. Accordingly, attempts have been made to utilize xenon flash lamps of the type which are available and to adapt them for use in semiconductor manufacture. It was observed, however, that the quality of the exposure produced by the available flash lamps, particularly the helical flash lamps was not as good as expected. Studies conducted by the inventor indicated to him that the quality of the exposure was degraded from what an ideal print source would produce. Further studies indicated that helical xenon flash lamps had assymetrical light output present in the anode and cathode axis of the xenon lamp.
The inventor determined that the primary reason for the assymetry is the presence of two very high current density spots located in close proximity to the anode and to the cathode of the helical flash lamp. At these locations the current density is in the neighborhood of 10.sup.6 A/cm.sup.2, resulting in a very high ultra-violet (UV) output from these points. Such UV radiation was traced as the source of the distortion in the photoresist.